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doc/html/_sources/pair_class2.txt
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doc/html/_sources/pair_class2.txt
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.. index:: pair_style lj/class2
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pair_style lj/class2 command
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============================
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pair_style lj/class2/cuda command
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=================================
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pair_style lj/class2/gpu command
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================================
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pair_style lj/class2/kk command
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===============================
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pair_style lj/class2/omp command
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================================
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pair_style lj/class2/coul/cut command
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=====================================
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pair_style lj/class2/coul/cut/cuda command
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==========================================
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pair_style lj/class2/coul/cut/kk command
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========================================
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pair_style lj/class2/coul/cut/omp command
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=========================================
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pair_style lj/class2/coul/long command
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======================================
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pair_style lj/class2/coul/long/cuda command
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===========================================
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pair_style lj/class2/coul/long/gpu command
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==========================================
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pair_style lj/class2/coul/long/kk command
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=========================================
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pair_style lj/class2/coul/long/omp command
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==========================================
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Syntax
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""""""
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.. parsed-literal::
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pair_style style args
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* style = *lj/class2* or *lj/class2/coul/cut* or *lj/class2/coul/long*
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* args = list of arguments for a particular style
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.. parsed-literal::
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*lj/class2* args = cutoff
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cutoff = global cutoff for class 2 interactions (distance units)
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*lj/class2/coul/cut* args = cutoff (cutoff2)
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cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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*lj/class2/coul/long* args = cutoff (cutoff2)
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cutoff = global cutoff for class 2 (and Coulombic if only 1 arg) (distance units)
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cutoff2 = global cutoff for Coulombic (optional) (distance units)
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Examples
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""""""""
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.. parsed-literal::
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pair_style lj/class2 10.0
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pair_coeff * * 100.0 2.5
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pair_coeff 1 2* 100.0 2.5 9.0
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.. parsed-literal::
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pair_style lj/class2/coul/cut 10.0
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pair_style lj/class2/coul/cut 10.0 8.0
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pair_coeff * * 100.0 3.0
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pair_coeff 1 1 100.0 3.5 9.0
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pair_coeff 1 1 100.0 3.5 9.0 9.0
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.. parsed-literal::
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pair_style lj/class2/coul/long 10.0
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pair_style lj/class2/coul/long 10.0 8.0
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pair_coeff * * 100.0 3.0
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pair_coeff 1 1 100.0 3.5 9.0
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Description
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"""""""""""
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The *lj/class2* styles compute a 6/9 Lennard-Jones potential given by
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.. image:: Eqs/pair_class2.jpg
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:align: center
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Rc is the cutoff.
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The *lj/class2/coul/cut* and *lj/class2/coul/long* styles add a
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Coulombic term as described for the :doc:`lj/cut <pair_lj>` pair styles.
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See :ref:`(Sun) <Sun>` for a description of the COMPASS class2 force field.
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The following coefficients must be defined for each pair of atoms
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types via the :doc:`pair_coeff <pair_coeff>` command as in the examples
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above, or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands, or by mixing as described below:
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* epsilon (energy units)
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* sigma (distance units)
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* cutoff1 (distance units)
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* cutoff2 (distance units)
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The latter 2 coefficients are optional. If not specified, the global
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class 2 and Coulombic cutoffs are used. If only one cutoff is
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specified, it is used as the cutoff for both class 2 and Coulombic
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interactions for this type pair. If both coefficients are specified,
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they are used as the class 2 and Coulombic cutoffs for this type pair.
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You cannot specify 2 cutoffs for style *lj/class2*\ , since it has no
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Coulombic terms.
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For *lj/class2/coul/long* only the class 2 cutoff can be specified
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since a Coulombic cutoff cannot be specified for an individual I,J
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type pair. All type pairs use the same global Coulombic cutoff
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specified in the pair_style command.
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----------
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If the pair_coeff command is not used to define coefficients for a
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particular I != J type pair, the mixing rule for epsilon and sigma for
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all class2 potentials is to use the *sixthpower* formulas documented
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by the :doc:`pair_modify <pair_modify>` command. The :doc:`pair_modify mix <pair_modify>` setting is thus ignored for class2 potentials
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for epsilon and sigma. However it is still followed for mixing the
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cutoff distance.
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----------
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Styles with a *cuda*\ , *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of the lj/class2 pair styles can be mixed.
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Epsilon and sigma are always mixed with the value *sixthpower*\ . The
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cutoff distance is mixed by whatever option is set by the pair_modify
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command (default = geometric). See the "pair_modify" command for
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details.
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All of the lj/class2 pair styles support the
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:doc:`pair_modify <pair_modify>` shift option for the energy of the
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Lennard-Jones portion of the pair interaction.
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The *lj/class2/coul/long* pair style does not support the
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:doc:`pair_modify <pair_modify>` table option since a tabulation
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capability has not yet been added to this potential.
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All of the lj/class2 pair styles support the
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:doc:`pair_modify <pair_modify>` tail option for adding a long-range
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tail correction to the energy and pressure of the Lennard-Jones
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portion of the pair interaction.
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All of the lj/class2 pair styles write their information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands do
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not need to be specified in an input script that reads a restart file.
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All of the lj/class2 pair styles can only be used via the *pair*
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keyword of the :doc:`run_style respa <run_style>` command. They do not
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support the *inner*\ , *middle*\ , *outer* keywords.
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Restrictions
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""""""""""""
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These styles are part of the CLASS2 package. They are only enabled if
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LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`
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**Default:** none
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----------
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.. _Sun:
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**(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998).
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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